1. Field of the Invention
The present invention relates to manipulating apparatus. More particularly, the present invention relates to a manipulator for vacuum hoses inside reactor pressure vessels.
2. Discussion of Background
A nuclear reactor facility typically has several areas where radioactive materials are stored or used. These areas are in the form of tanks, pools or vessels where the radioactive materials are kept under water that serves as both shielding and coolant, and additionally enables the radioactivity to be attenuated with the increased distance to operators who perform reactor and material operations. In the course of operations and handling of these materials, debris and tools may fall to the floor of these various areas and need to be retrieved or removed periodically to maintain the clarity of the water. Vacuuming is the removal method of choice for all but the largest items. Thorough vacuuming requires a systematic approach so that all areas are reached by the vacuum hose. Because of suspended material in the water, it is not always easy to see the floor to vacuum in a systematic way.
In some reactors, the design of the pressure vessel and its internal components are such that there is little room for the introduction and removal of vacuum equipment and any apparatus related to vacuuming or other operations that may from time to time be required inside a pressure vessel. One such pressure vessel design is a production reactor having an upper plenum with plugs for sealing access holes to each fuel assembly. At the bottom of this type of pressure vessel, on a lower plenum, are monitoring pins on which the fuel assemblies rest.
A particular criterion of manipulators sent into pressure vessels is the need to assure that apparatus introduced to the vessel can be removed in the event of a mechanical or electrical failure. This is especially important where the aperture to the vessel interior is small. If a particular apparatus fails and cannot be removed the way it was brought in, the consequences may be severe; a portion of the vessel may need to be dismantled or the apparatus cut up into smaller pieces remotely.
There are several apparatus for removing debris from the bottom of a pressure vessel or spent fuel pool, including apparatus that manipulate objects. See in particular the apparatus disclosed by Pullen in U.S. Pat. No. 4,995,138 and by Silverman et al. in U.S. Pat. No. 4,910,823. In addition there are other manipulators that meet specialized requirements, such as the extraction device of Guironnet disclosed in U.S. Pat. No. 5,011,206 and Horton, III's marine search and salvage system disclosed in U.S. Pat. No. 3,843,184. None of these apparatus, however, are designed to enter a small opening in an upper plenum and vacuum a large area of a pressure vessel in a systematic way and to do so with built-in, fail-safe features in the event the apparatus suffers a mechanical or electrical breakdown or is damaged in use.